Answer
$y = \frac{x^2}{6}-1.5$
We can see the graph below:
Work Step by Step
$r = \frac{3}{1-sin~\theta}$
$r-r~sin~\theta = 3$
$\sqrt{x^2+y^2}-y = 3$
$\sqrt{x^2+y^2} = y+3$
$x^2+y^2 = y^2+6y+9$
$x^2 = 6y+9$
$y = \frac{x^2}{6}-1.5$
We can see the graph below: